The dimensions of the lockers are as follows.
Small locker: 420 x 800 x 273 mm (~ 90L)
Large locker: 615 x 930 x 472 mm (~ 270L)
(https://community.bahn.de/questions/1582543-schliessfacher-frankfurt-hauptbahnhof-aktuelle-preise - please note that this information is from 2018)
If your bags can be arranged into that volume, then you should be fine.